A filling unit for filling containers with an aseptic pourable food product is known from US-A-2011/0023996.
In greater detail, the filling unit substantially comprises:                a carousel conveyor rotating about a rotation axis;        a tank containing the pourable food product; and        a plurality of filling devices supported by the carousel conveyor in a position radially external with respect to the rotation axis of the carousel conveyor.        
In greater detail, the carousel is provided with a plurality of gripping devices for gripping the neck of respective containers and moving the containers towards and away from the respective filling device.
Still more precisely, each gripping device comprises a pair of jaws which can be moved between an open configuration in which they receive or release the neck of the container, and a closed configuration in which they firmly grip the container.
Furthermore, when the jaws are arranged in the closed configuration, the gripping device can be moved along a vertical direction between:                a rest position, in which a mouth of the container is spaced from a pouring opening of the filling device; and        an operative position, in which the container is closer to the pouring opening and undergoes the filling operation.        
The filling unit also comprises a plurality of lifting devices which are operatively connected with respective gripping devices, so as to cause their movement along the vertical direction.
The known filling unit also comprises:                an aseptic area, in which aseptic conditions are preserved and where containers are filled with the pourable product;        a non-aseptic area; and        a wall, which divides the aseptic area from the non-aseptic area.        
The gripping devices and the containers are arranged in the aseptic area.
Each lifting device has a servomotor arranged in the non-aseptic area and a rod which is driven by the servomotor and is operatively connected to the relative gripping member.
In particular, the rod has a portion, which passes through the wall. There is therefore the risk that the portion of the rod drives non-sterile air inside the aseptic area, thus contaminating the latter.
In order to contain that risk of contamination, each lifting device comprises a bellow which is interposed between a fixed part of the lifting device and an end of the rod.
The end of the rod is arranged in the aseptic area and the bellow seals the portion of the rod arranged in the aseptic-area.
Still more precisely, each bellow is arranged between the relative gripping device and the pouring opening relative filling device.
Furthermore, each bellow is arranged over the mouth of the respective container.
There is therefore the risk that, due the inevitable leakage of the bellows, the non-sterile air can reach the mouths of the containers when the respective gripping devices are in the lowered position, and contaminate either the containers or the food product contained in the containers, thus affecting the asepticity of the filling operation.
A need is felt within the industry to improve as far as possible the asepticity of the pourable product filled in the containers.